How many words? There is so much to talk about here. It's quite an easy, broad question and you could choose to go many directions. Personally, I really like some of Bourdieu's work in this area so I'd use that as the theoretical framework, particularly his concepts of cultural capital and habitus. Some studies have been conducted in schools using these concepts which are really interesting and can be used to both support the claim in this question as well as nuance its significance.
My advice is:
1) get the theory down
2) criticise it
3) use a study to support and critique the question (they shouldn't be hard to find)
4) criticise the study
5) use another study, say how it's different
6) criticise the study
7) conclude saying it is relevant, but other variables are clearly important (as bourdieu shows through his concepts) and these other variables correlate with levels of schools, but these variables can be somewhat changed by the quality of the school (as shown in the studies) and cultural capital affects the type of school children might attend